Plug fuse



Sept. 3, 1935. G. R. GOODWIN PLUG FUSE Filed Feb. 13, 1934 Patented Sept. 3, 1935 UNITED STATES PATENT OFFICE PLUG FUSE Application February 13, 1934, Serial No. 711,009

8 Claims.

Vbuse which carries a central fuse terminal, the

top and base being held together by a thin metal shell constituting the other fuse terminal and having screw threads molded therein cooperating with external threads on the fuse top to clamp ith'top and base together and acting as external threads for cooperating with internal threads of a fuse-receiving socket. When the fuse element in such a fuse blows, the hot gases thus .generated produce a pressure within the fuse chamber, often suiiicient to extend the shell accordion fashion, and permit a. rapid venting of the hot gases within between the top and base to the atmosphere. One of the tests to which Afuses are submitted by the Underwriters Laboratorles is to surrolmd the fuse with absorbent cotton and then cause the fuse to blow. The cotton should not become ignited when this is done.

One object of the present invention is to provide means for so sealing Separate casing parts of the fuse, such as the top and base of a. plug fuse, that even though the blowing of the fuse should somewhat separate the parts, the hot gases are so sealed, or their escape is so eiiectually delayed, that the fuse may be confidently relied upon to successfully meet this Underwriters test.

Where the top of the plug fuse is made of glass kit has been found desirable to employ a sleeve of paper or the like within the tubular portion of the fuse top to protect it from the shattering eifects of the hot gases and molten metal when the fuse blows.

A further object of this invention, therefore, is to provide in a single element the protection of the glass from breakage and the sealing of the top and base to prevent too rapid escape of hot gases when theA fuse blows.

Further objects and advantageous constructions will appear from a more complete description of an embodiment oi' this invention shown in the accompanying drawing in which Figures 1 and 2 are central longitudinal sections through the fuse top and sealing sleeve, respectively.

Figure 3 is a side elevation partly broken away and in section of the fuse base.

Figure 4 is a perspective of the sealing sleeve.

Figure 5 is a view partly in elevation and partly in central longitudinal section through an embodiment of 4the completed fuse.

Figure 6 is a section on line 6 6 of Figure 5.

Referring to the drawing, at I is indicated a top portion for the fuse which is preferably made of glass. At one end it is shown as provided with a window 2 and extending away therefrom this top is provided with a tubular side wall 3. This tubular side wall is provided with external molded threads 4 thereon and in one plane the threads are cut away to form a groove 5 for a purpose which will later appear. 'I'he inside face of the tubular portion 3 is tapered, the smaller end as at 6 being positioned adjacent to the window 2 and the larger end as at I being at the open end of the tubular portion 3.

The fuse also has a base III, shown separately in Figure 3, which is provided centrally with a fuse terminal I I. It also is provided with an open ended tubular extension I2 which has its outer face tapered complementally to the taper of the portion 3 of the top I, the smaller end of the extension I2 being positioned at its upper end and remote from the terminal Il. Between the extension I2 and the terminal II. this base is provided with an outwardly extending flange I3.

Positioned between the top and base, when the parts are assembled, is a. sleeve or tube 2II of insulating and somewhat compressible fibrous material as a somewhat soft heavy paper which is shown detached in Figures 2 and 4. The outer diameter of this member is suiiiciently smaller than the outer end of the internal face of the tubular portion 3 of the top to permit this sleeve 20 to be freely inserted into and telescope the open end of the top. The internal diameter of the member 20 is also of such a size as to permit the ready insertion therein of the upper end of the extension I2 of the base, but the sleeve is of such thickness and the internal face of the top portion 3, and the external face of the extension I2 of the base are so related, that in order to seat the flange I3 against the lower edge of the tubular portion 3, as shown in Figure 5, suillcient pressure must be exerted to cause the member 20 in its final position to make a force t with both the top and base of the fuse.

'I'he fuse link 22 within the fuse casing has one end portion secured in any usual manner to the terminal II and passes from this terminal upwardly toward the Window 2 where its intermediate portion is preferably formed with a portion 23 of reduced cross section which localizes the rupturing point of the fuse when it blows. The other end portion of the fuse element then passes downwardly between the extension l2 and the porti-on 3 of the fuse top, and spaced by the sleeve 20 from the fuse top, and passes out between the flange i3 and the fuse top through a groove 25 in the latter. It then extends upwardly within the groove 5 and it is secured in any suitable way as at Z6 to the upper end of the metallic shell 3E! which forms the other terminal for the fuse element, This shell 3D has molded therein screw threads 3 I, which on their inner faces engage the threads 4 of the fuse top, and on their outer faces form external threads for engagement with internal threads of a fuse-receiving socket in the usual manner. The lower end of the metallic shell Se may have an in-turned ange 32 which engages beneath the shoulder or ange I3 of the base and holds the parts assembled.

When a fuse so made blows, the pressure produced by the hot gases within the casing between the top and base, while it may act to stretch the shell somewhat so that the base and top become slightly separated, fails to separate these parts to such an extent as to'perrnit free escape of these gases past the sealing element 2Q, which not only tends by its frictional grip on. the top and base to reduce the stretching of the metallic shell, but also maintains a relatively tight between the top and base throughout any slightl separation of the base and top which may occur.

- Thus the escape of the hot gases is so retarded,

even if not entirely prevented, that they cannot cause ignition of the absorbent cotton in which the fuse is placed when it is undergoing the Underwriters test hereinbefore described. It will also be noted that not only does this element act as an effective seal between the parts, but it also acts as a protector to prevent breakage of the glass top when the fuse element blows.

From the foregoing description of an embodiyment of this invention, it should be evident to those skilled in the art that various changes and modications might be made without departing from the spirit or scope of this invention as defined by the appended claims.

I claim:

l. A fuse having overlapping tubular casing portions, and packing material force-iitted between said portions where they overlap.

2. A fuse having top and base portions, one of said portions having a tubular part overlapping telescoping a part of the other portion, and packing material force-ritted between said parts.

3. A fuse having top and base portions provided with overlapping complementally tapered annular faces, and a sleeve of brous material compressed between said faces.

4. A fuse having a glass top provided with a tubular side Wall portion, a base having an extension projecting into said side wall portion, a fuse element having a portion lying between said side wall and said extension, and a sleeve of insulating material force-fitted between said extension and lower portion and spacing said fuse element from said wall portion.

5. A fuse having a top portion provided with a window in its end and a tubular side wall portion having its inner surface tapering with its smaller end adjacent to said window, said fuse having a base provided with a central fuse terminal and a tubular extension projecting within said side wall portion, the outer surface of said extension tapering with its larger end nearer to said fuse terminal, means for securing said base and top portion together, and a tube of fibrous material tightly engaged between said tapering surfaces.

6. A fuse having a top portion provided with a window, a base portion provided with a fuse element terminal, an external metallic shell, a fuse enclosed by said top, base and shell and secured at one end to said shell and at the other end to said terminal, said top and base having overlapping tubular portions, and sheet material sealing said top and base and having a forcefit between said overlapping portions.

'7. A fuse having a glass top provided with a window in its end and an externally threaded tubular side wall portion, said fuse having a base of insulating material provided with a centrall fuse terminal and a tubular extension projecting within said side wall portion, said base having a shoulder portion beneath said extension, a metallic shell having molded threads internally engaging the threads oi said top and having an inturned iiange engaging about said shoulder to hold said top and base assembled, a fuse element having one end attached to said terminal, an intermediate portion positioned back of said window, and the other end portion extending between said extension and wall portion and secured to said shell, and a sleeve of non-conducting brous material compressed between said extension and Wall portion and positioned between said fuse element and wall portion.

8. A fuse having a glass top provided with a window in its end and an externally threaded tubular side wall portion having its inner surface tapering with its smaller end adjacent to said window, said fuse having a base of insulating material provided with a central fuse terminal and a tubular extension projecting within side wall portion, the outer face of said extension tapering with its larger end nearer to said fui-'e terminal, said base having a shoulder portion. beneath said extension, a metallic shell having molded threads internally engaging thc threads o said top and having an in-turned flange engaging about said shoulder to hold said top and base assembled, a fuse element having one end attached to said terminal, an intermediate portion positioned back of said window, and the other end portion extending between said extension and wall portion and secured to said shell, a sleeve oi non-conducting nbrous material compressed between said extension and wall portion and positioned between said fuse element and Wall portion.

GEORGE R. GOODWIN. 

